ok so well i finally got the muffler put on today and my car is still popping/backfiring when at lower rpm's....also it stumbles coming off idle. is this because of the tune being off in the pcm since i haven't had it tuned since the build or does it sound mechanical. i drove it for about a week with just straight-pipes fwiw no muffler. it only wants to backfire when cold and when coming down to lower rpms. any advice? i want to make sure its in the tune before i spend the money. thanks to all

 

Only way to tell is to have it datalogged while the problem is happening. Double-check the connections of your plugs and plug wires for tightness.

 

My Lt1 has always had a backfire and pop through the exhaust when it's winding down. Try taking a video and uploading it.